1. Technical Field
The present invention relates to a sintered alloy which may be preferably used for, for example, turbo components of turbochargers, specifically, nozzle bodies that must have heat resistance, corrosion resistance, and wear resistance, and relates to a production method therefor.
2. Background Art
In general, in a turbocharger installed for an internal combustion engine, a turbine is rotatably supported by a turbine housing connected to an exhaust manifold of the internal combustion engine, and plural nozzle vanes are rotatably supported such that the nozzle vanes surround the outer circumference of the turbine. Exhaust gas flowing in the turbine housing flows from the outer circumference of the turbine into the turbine and is discharged in the axial direction, thereby rotating the turbine. A compressor is provided at the same shaft as the shaft of the turbine and is at a side opposite to the side with the nozzle vanes. Then, the compressor is rotated, whereby air to be supplied to the internal combustion engine is compressed.
The nozzle vane is rotatably supported by a ring-shaped part called a “nozzle body” or a “nozzle mount”. The shaft of the nozzle vane penetrates the nozzle body and is connected to a link structure. By driving the link structure, the nozzle vane is turned, and a degree to which a flow path is open is adjusted to allow exhaust gas to flow into the turbine. The present invention relates to turbo components that may be provided at a turbine housing, such as a nozzle body (nozzle mount) and a nozzle plate to be mounted on the nozzle body.
Since the above-described turbo components for turbochargers may be subjected to corrosive exhaust gas at high temperatures, the turbocharger must have heat resistance and corrosion resistance. In addition, since the turbo components slidingly contact a nozzle vane, the turbo components must also have wear resistance. Therefore, for example, a high Cr cast steel, a wear resistant material, and the like are conventionally used. The wear resistant material may be formed by performing a chromium surface treatment on a SCH22-type material, as specified by the JIS (Japanese Industrial Standards), in order to improve corrosion resistance. As a wear resistant component that has superior heat resistance, corrosion resistance, and wear resistance, and that is inexpensive, a heat resistant and wear resistant sintered component including carbides dispersed in a matrix of a ferrite stainless steel has been suggested (for example, see Japanese Patent No. 3784003).
Since the sintered component suggested in Japanese Patent No. 3784003 is obtained by liquid phase sintering, machining must be performed when the component is required to have high precision. However, the component is deteriorated in machinability since a large amount of hard carbides are precipitated therein. Therefore, improvement of machinability has been desired. The components of turbochargers are typically made from an austenitic heat resistant material. On the other hand, a turbo component for a turbocharger disclosed in Japanese Patent No. 3784003 is made from a ferritic material. In this case, the turbo component has a different thermal expansion coefficient from that of surrounding components, whereby a gap is readily formed between the components made from each material, and attachment of these components is insufficient. Therefore, the design of the turbo component is difficult for practical use, and the turbo component is required to have a similar thermal expansion coefficient as that of the surrounding austenitic heat-resistant material.